This invention relates to the art of power wrenches and more particularly to a mechanism for gripping fiberglass pipe as it is rotated by power tongs.
The prior art contains many diverse jaw constructions for power tongs, most of which include jaws having serrated faces designed to bite into the surface of a pipe and means for applying radially inward force to the jaws as the power tongs operates. As a consequence, most prior art tongs' jaws cause substantial damage to the surface on the pipe upon which they are used. With standard pipe materials, this is ordinarily not a problem; however, with particularly soft materials, it may be, and the inventors have already proposed a power tongs jaw construction designed to avoid surface damage. That invention is disclosed in U.S. patent application Ser. No. 886,195 filed July 9, 1986 which is incorporated herein by reference. That application is intended particularly for soft metallic pipes. Modern non-metallic well pipe, for example fiberglass pipe which is manufactured by winding layers of fiberglass and plastic to form a tube, presents an entirely different set of problems, and it is this type of pipe to which the present invention is directed.
If traditional cam actuated toothed jaws are used on fiberglass pipe, too much pressure is concentrated at the points where the jaws contact the pipe, and this can cause the plastic and fiberglass layers to crack and separate.
It is therefore an object of this invention to spread out the gripping pressure over the entire circumference of the pipe and this object is achieved by using a chain or strap wrench to apply torque to the pipe.
A second object of the invention is to avoid causing surface damage to the fiberglass pipe by eliminating the need for toothed dies.
These and other objects are achieved by the present invention, which comprises in combination a power tong having a rotating head, a plate for mounting concentrically upon said head, means for rotatably retaining said plate upon said head, a post extending vertically from said plate, a flexible member having two ends, one of which is attached to said post and the other of which has engagement means thereon, said flexible element being of sufficient length to encircle a pipe of a predetermined diameter which is to be rotated by the tongs, a pin extending vertically from said plate, a lever pivotally mounted upon said pin, said lever having two ends on opposite sides of said pin, one of said ends comprising a finger adapted to contact said engagement means on the flexible element and the other end of said lever forming an actuating arm, and a rod extending vertically from said rotating head, said rod being positioned to engage the actuating arm of said lever.